Method for dehydrating green crop

ABSTRACT

The green crop is compressed and, during the compressing operation, is heated to a temperature of at least about the boiling point of water at the prevailing gas pressure; and the moisture emitted from the crop as a result is allowed to escape. Preferably, the green crop is held compressed during part of the time when steam is leaving it due to the heating, whereby a selfsustained or coherent end product is obtained.

Q United States Patent 1 1 3,559,566

[72] Inventors John Axel Aspegren [50] Field of Search 100/35, 37,Stockholm; 38, 92. 93, 98, 232, 110; 34/14, 39,15,16

Jan Anders Askling, Tullinge; Lars-lngvar Larsson, Tullinge, Sweden [56]References (med [2] Appl. No. 682,801 UNITED STATES PATENTS I Filed 14,1967 729,149 5/1903 Fenn (PelL/Digest) 1 Patented 2, 1971 2,393,130l/l946 Toulmin, Jr. (PelL/Digest) Asslgnee Alia-Laval AB 3,352,229 1H1967 Morse 100/38 Tumba, Sweden a corporation of S ed PrzmaryExaminer-Peter F eldman [32] Priority No 18, 1966 Att0meyDavis, Hoxie,Faithfull & Hapgood [33] Sweden [31] 15807/1966 ABSTRACT: The green cropis compressed and, during the compressing operation, is heated to atemperature of at least [54] F gg DRATING GREEN CROP about the boilingpoint of water at the prevailing gas pressure; 9 Chums rawmg and themoisture emitted from the crop as a result is allowed [52] US. Cl100/38, to escape. Preferably, the green crop is held compressed dur-34/39, 100/93, 100/ 1 10, 100/232 ing part of the time when steam isleaving it due to the heating, Int. Cl 1330b 15/34 whereby aself-sustained or coherent end product is obtained.

5 6 3 4a 10 512 H? I r I l l I METHOD FOR DEl-IYDRATING GREEN CROP THEDISCLOSURE The present invention relates to a method of dehydratinggreen crop in an artificial way. The need for artificial or forceddehydration of green crop has arisen mainly because the green crop, ifleft on the field for too long a time in bad weather, can partly loseits nutritives or even become quite spoiled.

According to known methods of forced dehydration of green crop, hot airis usually used for evaporation and extraction of water contained in thegreen crop. Generally, the moist green crop is supplied into a stream ofhot air and carried along in this stream until the water content hasdecreased to a desired value. However, the equipment used for carryingout this method is rather large and is unsuited for the desired mobility on the field. Consequently, green crop to be dehydrated accordingto this method must be collected on the field and then transported tothe nearest equipment installation for dehydration. This isdisadvantageous because it requires expensive transport capacity totransport a material consisting mainly of water which is subsequently tobe removed (newmown green crop generally has a moisture content of about70-80 percent by weight).

The principal object of the present invention is to provide a new methodof dehydrating green crop, which method can be performed by means of anapparatus adapted to be made unusually compact and therefore bettersuited than prior dehydrating equipment for moving around on the field.

The method according to the invention comprises the steps of compressingthe green crop, heating the green crop during the compressing operationto a temperature of at least about the boiling point of water, andallowing moisture contained by the crop to leave.

If the squeezing pressure is released at a relatively early stage of thedehydrating process, the green crop after finished dehydration willreturn to its original free or porous state. On the other hand, if thegreen crop is compressed also during a part of the time in which steamis leaving the crop, the advantage can be achieved that the green crop,its withdrawal from the dehydrating apparatus in a sufficiently drystate, will remain in its compressed state. This, of course, greatlyfacilitates the transportation of the crop from the field, and it alsomakes it possible to obtain finished wafers, so called briquettes. Inthe case of dehydrated green crop which initially has had a moisturecontent of more than 40 percent, it can be maintained in a compressedcondition by heating the green crop, during the compression, to atemperature between 100 and 170 C. The particular temperature selectedin this range will depend upon (1) the kind of green crop, (2) thepressure to which the green crop is subjected during the dehydration,and (3) the time during which it is subjected to the said pressure. Due,among other things, to the risk of discoloring (scorching or burning) ofthe green crop, the most suitable temperature is considered to liebetween l and 120 C.

The green crop may be heated either indirectly or directly. Indirectheating may be performed either by means of a heating medium, such assteam, or electrically. Direct heating may be performed, for example, bytransporting the green crop through a field of electromagnetic waves.The last-mentioned method of heating the green crop is especiallyadvantageous because it substantially eliminates the risk ofdiscoloring, since dehydrated crop cannot be heated by electromagneticwaves to a temperature which is critical for the crop.

According to the invention, an apparatus for performing theabove-described method comprises means for compressing the green crop,means for heating the green crop during the compressing operation to atemperature of at least about the boiling point of water at theprevailing gas pressure, and means for allowing moisture contained bythe green crop to leave the pressure chamber while the crop iscompressed.

In connection with indirect heating of the green crop, the walls of theaforesaid pressure chamber are arranged to be heated by a heatingmedium, such as steam, or electrically. In

connection with direct heating of the green crop, means are arranged toprovide a field of electromagnetic waves within the pressure chamber.

In order to lead away moisture emitted from the green crop, the walls ofthe pressure chamber are provided with openings which may be arranged tobe closed during a part of the dehydration process.

An advantageous form of the pressing chamber for indirect as well asdirect heating of the green crop is a channel which is substantiallyannular in cross section and having walls provided with openings along apart or the whole of its length.

By means of the abovedescribed apparatus, the new method can beperformed either as a continuous or as a discontinuous dehydrationprocess. In an apparatus arranged for a continuous dehydration process,the pressing channel may be so arranged that the green crop first passesalong a wall portion with openings for the removal of liquidmechanically pressed from the green crop, then passes along a secondwall portion without any openings, and finally passes along a third wallportion with openings for leading away steam emitted from the green cropdue to the heating of the same. Preferably, the pressing channelconverges in the pressing direction along a part of the whole of itslength.

One embodiment of the apparatus according to the invention, chosen as anexample only, will be described in the following with reference to theaccompanying drawings. In the drawings, FIG. 1 is a longitudinalsectional view, somewhat schematic, of an apparatus according to theinvention for continuous dehydration of green crop; FIG. 2 is asectional view along the line Il-II in FIG. 1; and FIG. 3 is a diagramillustrating the results of a number of tests concerning dehydration ofgreen crop in accordance with the present invention.

The apparatus shown in FIG. 1 comprises means for compressing greencrop, a pressing chamber in which the green crop is to be compressed,means for heating the walls of the pressing chamber, and means forallowing moisture contained by the green crop to leave the pressingchamber.

The means for compressing the green crop comprises two plungers orpistons l and 2, which are arranged in a housing or cylinder 8 having aninlet passage 8a through which the green crop is supplied in thedirection of arrow P (FIG. 1) to the space opposite piston l. The twopistons cooperate to force the green crop into the pressing chamberwhich in this case is constituted by a channel 3 of generally annularcross section. The cannel 3 is formed between an inner cylindricalmember 5a and an outer cylindrical wall 6. The means for heating theouter and inner walls of channel 3 comprise a jacket 4a surrounding theouter wall 6 of the channel to form a space 4, there being another space5 within the inner member 5a. These spaces 4 and 5 are arranged forthroughflow of a heating medium, such as steam or oil heated to atemperature of about C. or more. The heating medium inlet and outlet forthe jacket space 4 are shown at 9 and 9a, respectively. The inlet andoutlet for the other heating space S are not shown but may be arrangedin any suitable way.

The walls of pressing channel 3 are provided with openings 60 along apart or the whole of its length for allowing moisture contained by thegreen crop to leave the pressing channel. By way of example, pressingchannel 3 in the pressing direction may be provided with a first wallportion 3a having openings 6a, a second wall portion 312 withoutopenings, and finally a third wall portion 30 having openings 6a. Theseopenings are shown, by way of example, as being formed by tubes leadingfrom channel 3 through jacket space 4 to the outside of the latter.

ln dehydrating green crop by means of the above-described apparatus,fresh or slightly dried green "crop is supplied to the housing spaceopposite the piston 1, as by means of a conveyor or other transportmeans. From this space the green crop, first by means of piston l andthereafter by means of piston 2, is forced into the annular pressingchannel 3. In the pressing channel, the green crop is graduallycompressed while being heated by the outer as well as the inner walls ofthe pressing channel, these walls in turn being heated by a heatingmedium (in this case superheated aqueous steam) flowing through thespaces 4 and 5. The squeezing pressure to which the green crop will besubjected within the pressing channel 3 may be controlled in advance bythe forming of the channel. Depending upon requirements, the channel maybe formed more or less converging along a part or the whole of itslength.

A dehydration process during which the green crop is continuously movedforward through the channel 3 may be as follows: (1) fresh green crop issupplied to' the first part 311 of the pressing channel, wherein anywater released by the mechanical compression of the green cropdischarges through the openings 6a in the first wall portion 3a of thechannel, (2) the green crop is heated so that moistureretained by thegreen crop is evaporated, a certain internal pressure being built up inthe part 3b where the pressing channel has no openings, (3) the steam.thus formed leaves through the openings in the third wall portion 3c ofthe pressing channel, and (4) the dehydrated crop leaves the pressingchannel in the form of one or more self-sustaining rods which 'are cutinto desired lengths. The cutting means is schematically illustrated inFIG. 1 by the arrow Q. Also schematically illustrated in FIG. 1 is thefact that jacket 4a does not necessarily extend along the whole lengthof pressing channel 3. It may be desirable to allow the crop, afterhaving been heated, to be transported within an unheated section ofchannel 3 so as to assure that the compressed end product will maintainits form as it leaves channel 3. Further, it may be desirable to keepthe final portion of the heated walls of the pressing channel 3 at alower temperature than that prevailing in the upstream portions of thepressing channel so as to avoid scorching or burning of the crop afterit has been partly dehydrated.

Test runs have shown that any noticeable self sustainment or coherencyof the constituents of the dehydrated end product cannot be achievedwith green crop having a moisture content as high as 40 percent or more,if it is not heated to a temperature of about 100 C. (i.e. the boilingpoint of water) or more, even if a very high squeezing pressure (360kp/cm?) and/or a long pressing time (6 min.) is used. It is not yetquite clear why an acceptable self-sustainment of the crop is obtainedat temperatures at or above 100 C. It probably depends on complicatedchemical and physical conditions. As the principal object of the presentinvention is to provide a method of rapidly and effectively dehydratingnew-mown or relatively new-mown green crop, temperatures exceeding 100C. are especially advantageous, as such a dehydration at temperaturesbelow the boiling point of water would be too time consuming. Test runstherefore have been confined to treatment temperatures exceeding 100 C.I

The diagram of FIG. 3 illustrates the results of a number of test runsin which green crop was dehydrated at different pressures andtemperatures. The initial material used in connection with the test runswas green crop having a moisture content of about 70 percent by weight.The horizontal axis of the diagram shows the squeezing pressure inkp/cmF, and the vertical axis shows the moisture content in percent byweight of the crop after the dehydration process. The curves in thediagram are indicated at A through G, and the following table shows thepressing times used (in seconds) and the temperatures to which the wallsof the pressing chamber were heated in connection with the test runsaccording to the different curves.

'The temperature within the green crop was measured during thedehydration process, and in all cases the temperature at least during apart of the pressing time was about C. or more.

In the diagram of FIG. 3 is also shown a horizontal dotted line H. Thisline, representing a moisture content of the treated crop of about 40percent by weight, is the upper limit for acceptable moisture content ofcrop having been dehydrated in accordance with the present invention.Also, with respect to the self-sustainment or coherency of thesubstituents of the end product, this line constitutes a limit overwhich acceptable wafers or briquettes could not be obtained.

Of course, the above-described test runs are insufiicient for statingoptimal values for the different elements cooperating in connection withthe dehydrating operation (as a matter of fact, these values varybetween different kinds of green crop), or for stating how far thedehydration can be carried by the practice of the present invention. Thedehydration can probably be carried farther than as shown by theabovedescribed test runs.

In FIGS. 1 and 2, reference numeral 10 designates radial webs supportingthe inner cylindrical member 50 within the surrounding cylindrical part6. The webs 10 thus divide the pressing channel 3 into subchannels ofarcuate cross section,

a s shown in FIG. 2.

I claim:

1. A method of dehydrating green crop generally having a moisturecontent of at least about 70 percent which comprises the steps ofcompressing the green crop, heating the green crop while undercompression to a temperature of atleast about the boiling point of waterat the prevailing gas pressure, and causing moisture contained by thegreen crop to leave the same and thereby provide the crop with a reducedmoisture content not in excess of about 40 percent.

2. The method according to claim 1, in which the green crop is heldunder compression during emission of steam from the crop, to obtain anend product which is self-sustained or coherent.

3. The method according to claim 1, in which said compression of thegreen crop is sufficient to obtain an end product adapted to be formedinto briquettes without further compression.

4. The method according to claim 1, in which said heating is carried toa temperature between l00 C. and 170 C.

5. The method according to claim 1, in which said heating is carried toa temperature between 1 10 C. and C.

6. The method according to claim 1, in which said heating is effectedindirectly.

7. The method according to claim 1, comprising also predehydrating thegreen crop by squeezing to a moisture content of 50 to 70 percent priorto said steps.

8. The method according to claim 1, in which the green crop iscompressed into an elongated body which is substantially annular incross section, said heating being effected from both the inside and theoutside of said body.

9. The method according to claim 8, comprising also dividing saidelongated body into rods during said compressing, and cutting said rodsinto desired lengths.

1. A method of dehydrating green crop generally having a moisturecontent of at least about 70 percent which comprises the steps ofcompressing the green crop, heating the green crop while undercompression to a temperature of at least about the boiling point ofwater at the prevailing gas pressure, and causing moisture contained bythe green crop to leave the same and thereby provide the crop with areduced moisture content not in excess of about 40 percent.
 2. Themethod according to claim 1, in which the green crop is held undercompression during emission of steam from the crop, to obtain an endproduct which is self-sustained or coherent.
 3. The method according toclaim 1, in which said compression of the green crop is sufficient toobtain an end product adapted to be formed into briquettes withoutfurther compression.
 4. The method according to claim 1, in which saidheating is carried to a temperature between 100* C. and 170* C.
 5. Themethod according to claim 1, in which said heating is carried to atemperature between 110* C. and 120 * C.
 6. The method according toclaim 1, in whiCh said heating is effected indirectly.
 7. The methodaccording to claim 1, comprising also predehydrating the green crop bysqueezing to a moisture content of 50 to 70 percent prior to said steps.8. The method according to claim 1, in which the green crop iscompressed into an elongated body which is substantially annular incross section, said heating being effected from both the inside and theoutside of said body.
 9. The method according to claim 8, comprisingalso dividing said elongated body into rods during said compressing, andcutting said rods into desired lengths.